Method of and apparatus for applying an anticorrosion coating to a hot-formed metal body

ABSTRACT

A hot-formed metal body emerges from a hot-forming stage in a solid, relatively scale-free, and hot condition and passes immediately into a treatment chamber prior to any substantial scale formation thereon. In this chamber a powder is sprayed on the body which, on cooling, forms a glassy, enamel-like coating on the body. After thorough cooling of the body, the coating is stripped off in a straightening apparatus and the body is recoated with a protective, relatively-long-lived coating or retains a coating, e.g., of zinc, applied with the temporary enamel coating.

United States Patent 1 Schaumburg 1 Jan. 30, 1973 [54] METHOD OF AND APPARATUS FOR APPLYING AN ANTICORROSION COATING TO A HOT-FORMED METAL BODY [76] Inventor: Georges Schaumburg, 1 bis, rue de Londres, Montigny-les-Metz, France 221 Filed: June23, 1969 21] Appl.No.: 836,224

[30] Foreign Application Priority Data June 25,1968 Germany ..P 17 71 677.7

[52] US. Cl ....,l,l7/ 50, 29/33 R, 29/33 P, 72/46, 117/6, 117/53, 117/104, 117/129 [51] Int. Cl.- ..B44d 1/34,C23f 15/00 [58] Field 01Search....117/53, 6, 50,129, 70 C, 128, 117/104; 29/33 R, 33F; 72/46 [56] References Cited UNITED STATES PATENTS 1,488,992 4/1924 Lewis ..1 17/6 2,442,485 6/1948 Cook ..l17/53 Bell ..1 17/128 3,328,145 6/1967 McMilan et al. ....1 17/129 3,454,433 7/1969 Mueller ..117/6 1,506,089 8/1924 Shuster .ml 17/104 R 2,974,051 3/1961 Moore ..1 17/129 3,012,732 12/1961 Kempthrone 239/300 3,037,878 6/1962 Cowleset a1. 117/129 3,110,571 11/1963 Alexander 117/129 3,154,426 10/1964 Kohnken ..1 17/129 Primary Examiner-Alfred L. Leavitt Assistant Examiner-Janyce A. Bell Attorney-Karl F. Ross [57] ABSTRACT A hot-formed metal body emerges from a hot-forming stage in a solid, relatively scale-free, and hot condition 5 Claims, 7 Drawing Figures PATE'NTEDJAN 30 I915 SHEET 10F 4 INVENTOR. 6502 Gas SCHAVHBUEG ATTORNEY VFIG.3

INVENTOR. GEORGES SOHAUHBUQG BY i2 4;

ATTORNEY PATENTEDJAIBO m 3. 713.866

. v SHEET 4 OF 4 Z reducing F I G 4 INVENTOR.

- GEOQGES SCHAUMBUEG ATTORNEY 1 METHOD OF AND APPARATUS FOR APPLYING AN ANTICORROSION COATING TO A HOT- FORMED METAL BODY l. FIELD-OF THE'lNVENTlON 2. BACKGROUND OF THE INVENTION In order to apply a coating such as paint, metal, lacquer or synthetic resin to a hot-formed metal body,

ing composition, dispensed in the liquid or solid state and merely solidifiable -on the body and/or fusiblethereon utilizing the heat of the body, surprisingly is 1 capable of providing a layer capable of thoroughly preventing a scale layer from forming. The enamel layer does not remain as tenaciously upon the body as would a slag layer or otherscale-forming material, but

particularly to a hot-rolled body, it is usually necessary to cool the body, then painstakingly descale it, and finally to otherwise coat or paintit. This descaling operation, usually carried out by pickling or sand-blast- I ing, is not only quite difficult, but it acts as a sizable bottleneck in the production of such metal bodies and cannot generally be carried out at the rate at which the bodies emerge from the final hot-forming stage.

v3. OBJECTS DYE-THE INVENTION rather can be broken away'w'ith ease as will be apparent hereinafter.

While reference has beenmade above to enamel and glass-like material as capable of fulfilling the requirements of the present invention, it may be noted that numerous enamel compositions which are capable of melting at a wide range of temperatures including the temperatures at which the metal (steel) body emerges from the hot-forming stage, are known and may be used in accordance with the present invention as long as the material is applied to the body with a viscosity sufficiently low to enable the liquid material to flow into a uniform thin film completely coating the body.

It is, therefore, the general object of the present invention to provide an improved method of and apparatus for applying an anticorrosion coating to a'hotformed body. a

It is also an object of the invention to provide a method of zinc-coating a body of steel or the likehaving a tendency to scale in ambient conditions.

More specifically, an object of the present invention is to overcome the above-mentioned drawbacks in coating a'hot-formed body, particularly a hot-rolled metal body. I

This film, which may have a thickness of the order of microns, e.g. 5-10 microns, may either be applied'in the form of a liquid coating or glass or may be applied in a powder stream, e.g., designed to fuse to flow along the surface at the temperature of the body, but in either case will-be a glassy substance. The enamel-forming material'and the anti-corrosion substance are applied continuously at the rate at which the body emerges from the final hot-formin g stage. v When powders are used, it is preferred to direct them againstthe' body in high-velocity aerosol-type jets, the velocity being controlled by compressed or pressurized air, a reducing gas'or an inert gas, e.g., nitrogen. At sufficiently high velocity, the powder effectively Still another object is to provide an improved system for continuously treatinga steel or similar body at the rate at which it emerges from the final shaping stage.

4. SUMMARY OF THE INVENTION preferably the last two rolls in the hot-rolling train of a rolling mill, in a relatively scale-free, solid, and hot condition and passes directly into a treatment chamber. A

powder consisting of a mixture of reducing agents and metallic oxides which fuse at the temperature of: the body issprayed against the body as it passes continuously through this chamber. The powder melts and, as the body cools,- solidifies into an enamel like coating which prevents the. body from scaling further. Thereafter or concurrently with the application of the enamel-like coating, a protective and more'permanent layer of an anticorrosi-on medium is applied, once the danger'of. scalingis past. Prior to or after formation of the anticorrosion film, e.g. of synthetic resin, lacquer, paint or a-protective metal such as zinc, the temporary enamel layer is. broken away and completely removed.

, A key feature of the presentinvention is the formation of temporary glass-like coating upon the surface of a hot-formed body while it is still in the heated condition and susceptible to scaling, of a relatively thin and brittle character upon c'ooling. This enamel layer, which may be composed of any conventional enamelpenetrates the surface skin of the metal, which 'can be assumed to be substantially free from scale, and is rapidly heated by' its intimate contact with the metal to the melting point of the powder and thereabove, whereby the molten droplets coalesce to form a liquidglass film upon the surface of the metal. Preferably, this treatment is carried out in a tubular chamber enclosing the body and open at its ends to permit the body to pass through the chamber. The latteris provided with a configuration geometrically similar to that of the body, i.e., a chamber of circular cross-section when the body is a continuously cast rod of circular cross-section or rectangular cross-section when the body is a rolled I slab.

As noted .earlier, an important feature ofthis invention resides in the provision of reducing agents in the treatment process to. eliminate any scale which may have been formed on the .hody prior to coating with the enamel layer. Thus','.the body may be treated with a reducing gas after leaving the final hot-forming stage or with reducing'agents,je. g., sodium,potassium and like reducing metals'incorpo'rated in the aerosol powder, the reduction products'and the oxidized metal compounds resulting from the reducing reaction being in- In applying the powders, preferably in the form of a powder mixture of the character set forth above, it has been found to be advantageous to provide a tandem array of blowers, the first receiving a mixture of pow ders and ,air and constituting a loosening meansv whereby the powders are dispersed in the air stream to form a flowable mixture. In the second or downstream blower, the powder/air mixture is accelerated to a high velocity and propelled to a discharge nozzle trained upon the hot-metal surface. Between this nozzle and the second blower, there may be provided a venturi injector to which compressed air is fed to regulate the velocity of the powder/air mixture directed against the workpiece surface.

While the invention is effective with hot-formed metals of any type, it has been found that hot-rolled products deriving from a rolling mill in which hot ingots or blooms are rolled in a heated state, and continuous casting arrangements offer the best sources of the bodies which are treated in accordance with this invention. Of course, the steps enumerated above apply whether the bodies are rolled or continuously cast, and either type of body may be subjected to thesubsequent treatment as indicated earlier to form a final and more or less permanent coating therein.

When the anticorrosion layer is applied subsequent to the temporary enamel layer, the latter may be broken away in a straightening mill (i.e. between rollers thereof) and conventional; coating materials (e.g. paints, lacquers and solvent-borne or flowable resins) effective upon a thoroughly cooled surface may be applied as noted below. The enamel may also be removed while the body remains warm but below scaling temperatures in which case anticorrosion layers of the type customarily used for hot application may be employed preferably, however, zinc'borate or a like compound, decomposable to form a coating metal, in this case zinc, may be incorporated into the enamel-forming substance to produce the metal in situ. Zinc, for example, applied as zincborate, alloys with the surface of the metal and remains as an effective anticorrosion coating once the enamel is removed.

The treatment chamber, according to further specific features of the present invention, is fitted with at least one nozzle which is connected through at least one blower to a hopper containing the above-described powder. The nozzle is formed with a Venturi restriction and a small pipe opening longitudinally into the nozzle is connected to a source of gas under pressure to-accelerate the powder and project it out of its nozzle against the body. An inert gas, a reducing gas, or simply air can be used as propellant.

The powder can be a mixture of oxides of Silicon, magnesium, aluminum, and iron, along with metallic sodium,'boron, orpotassium, or a compound of these chemicals. Zinc borate, according to a further feature of the invention, has proven useful in the enamel layer in that the final product is effectively zinc coated upon removal of the coating as noted earlier.

In accordance with yet another feature. of the invention, the coated and cooled body can be stripped of its temporary glassy coating, for instance'in the straightening station, and subsequently recoated for greater permanence by spraying with paint, lacquer, a syntheticresin protective coating, or the like. Such a method is particularly advantageous in that the glassy coating is quite easy to remove from the body, i.e., more'easily removed than the scale, so that the body can be completely processed in one continuous operation.

Prior to the original coating, it is possible to subject the body to treatment with a reducing agent, such as hydrogen carbon monoxide or methane, to remove any slight scales thereon. In this case, there is no need to admix reducing agents, such as powdered reducing metals, with the powder.

In an alternative embodiment the body, which can be a continuous rod, wire, sheet or the like, is simply passed through a fluidized bed of the above-described metal and metal-oxide powders to coat it.

5. DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become more apparent from the following description, reference being made to the accompanying drawing, in which:

FIG. 1 is a perspective view of a rolling mill embodying the principles of the present invention;

FIG. 2 is a vertical section through the rolling mill of FIG. 1;

FIG. 3 is a perspective view of a continuous casting installation embodying the principles of the present invention; 7

FIG. 4 is a vertical section through FIG-3;

. FIG.. 5 is a vertical section through an other apparatus embodying the present invention; and

FIGS. 6 and 7 are sections through a metal body at two separate stages in its treatment according to, the present invention.

6. SPECIFIC DESCRIPTION As seen in FIGS. 1 and 2, aslab or sheet 3 is formed between two rolls 23 and 23' of a last rolling stage 1 of a rolling train. Thisslab 3 emerges from between these rolls 23 and. 23 in a very hot, solid, and'relatively scalefree condition. It is transported by driven rollers 2 through a chamber 22 where it is subjected to the reduction effects of a reducing gas, e.g., hydrogen,carbon monoxide, methane or mixtures thereof, to remove any slight scale formations which might have come into being thereon.

The slab 3, still hot, then enters an inlet 4a of a treatment chamber 4. As it passes through this chamber 4 it is contacted on all its surfaces by a powder P which is a mixture of reducing-metal and metal oxide particles that fuse on the surface and form a very hard, infelxible enamel-like glassy coating C (see FIG. 6).

In addition, other substances (e.g. zinc) needed for the later surface treatment of this body can be added to this powder in the form of the material itself or as another substance (e.'g. zinc borate) which produces the installation of I the desired coating or alloying substance in situ.

These powders are held in a hopper 11 which is closed by a vane 17 and connected through a conduit 12 to a funnel 26 feeding a first aerating blower 9 in turn connected to a second driving blower 10. A conduit 13 leading from this second blower 10 is formed with a Venturi restriction 15 just downstream from the end of a narrow pipe 14 into which compressed air is fed. Thence the aerosol particles P are expelled through a nozzle 8 onto the slab 3 all around the latter. Thus, another nozzle 18 can be connected also to the blower l and the pipe 14 to cause-the fine particles P to impinge against the underside of the slab 3 in a region 27 free of rollers 2.

After the treated slab 3 exits through an outlet opening 4b of the chamber 4 it passes along a region 5 where it cools and the coating becomes very hard. FIG. 6 shows the slab 3 with its hardened coatings C.

Further downstream the slab 3 passes through a straightening station 6 where three rollers 28a-c bend the slab 3 sufficiently to break free the coating C.- Due to the substantially constant thickness of this coating, it is easily removed. This coating however adheres strongly to the metal body 3, since the surface of the body 3 reacts to some extent with the melted powders P to form the coating C.

Finally a coating station 7 having a plurality of nozzles 7a sprays a more flexible protective coating M, e.g. paint, upon the surface of the cooled slab 3. This coating M is shown in FIG. 7.

Because of the thinness of the coating C, any flaws, as shown at F in FIG. 6, will not be covered; the coating C will break in the region of these flaws F. Thus, an observer in the region 5 can clearly see them and mark the slab 3 in this region so that it can be later discarded.

In this manner, the flaws are easily recognized and there is no need to do a major descaling of the sheet 3, since any slight scales are removed by the gas in the chamber 22 or the oxides sprayed against it in the chamber 4 and, for the rest of the cooling time, the sheet 3 is covered by a very tight, nearly continuous glassy coating. Removal of this coating C has been found to be very simple once the sheet 3 is fully cooled and further scaling is no longer a problem.

FIGS. 3 and 4 show an alternative embodiment of the present invention. I-Iere, molten metal is poured from a ladle 16 into a funnel 1a on top of a mold I of a continuous casting installation. A metal body in the form of a thick wire 3' leaves the base of this mold 1' and is bent through 90 by driven rollers 2 of hyperbolic profile and through a chamber 22' similar to the chamber 22 of FIGS. 1 and 2.

A box-like chamber 4 is equipped with two nozzles 18 and 8 connected through a powder-aerating apparatus to a hopper 11 just as in FIGS. 1 and 2, common reference numerals referring to common struc ture. This wire 3' is here coated according to the method and principles set out in connection with FIGS. land 2. 7

As the wire 3' leaves the box 4', it is gripped between rollers 5.

In this embodiment the enamel coating is not stripped off the wire 3, since it serves to protect the wire during shipping and handling, and is relatively easily removed when desired. This coating also serves to accentuate and make more visible flaws in the surface of the wire 3, as described above for FIGS. 1 and 2. The subsequent anticorrosion coating may be applied as described above in connection with FIGS. 1 and 2 or zinc borate may simply be incorporated in the enamel-forming layer.

FIG. 5 shows a further embodiment of the invention having in this case a treatment chamber 4". Here a fluidized bed is formed around a continuous workpiece 3" riding on rollers 2". The workpiece 3" is very hot and relatively scale free. A blower 21 having an output connected through a conduit 20b to the bottom of the chamber-4" and an input conduit 20a connected to the top of this chamber 4 to fluidize minute metallic and metallic oxide particles fed into the chamber through a conduit connected to a hopper 11" above the chamber 4". In this way the workpiece 3" is very efficiently covered by the powder, so that it can move at high speeds through the chamber 4" and still be adequately coated. I

7. SPECIFIC EXAMPLES Example A -A steel body is hot formed and enters the treatment chamber at a temperature somewhat below its melting point. It is sprayed with a mixture of powders such that substantially equal parts of SiO A1 0 Fe O CaO MgO, Na, K, and B mixed with and carried by air strike the surface of the body. This mixture reduces the slight scale on the surface and fuses to form a glassy enamellike coating over the entire exterior of the body, the fused mixtu re flowing to cover allof its surface to a thickness on the order of say 5 to 10 microns. As the body cools, the enamel coating breaks in the region of any flaws on it.

Example B A steel wire is formed by rolling and enters a treatment chamber as above. In this chamber it is sprayed with the powder to which an equal proportion of zinc borate is added. The hard, enamel-like coating is formed as above. Then the body is fed through a straightening apparatus which removes the coating, and is found to be zinc coated in the sense that zinc is alloyed with surface zones of the metal body.

lclaim:

1. In the production of a metal body wherein the body emerges from a hot-rolling stage in a hot, solid, and relatively scale-free condition, the improvement comprising the steps of:

progressively applying to the exterior of said body, as

I it emerges from said hot-rolling stage in its hot condition prior to substantial scale formation on said body and immediately upon such emergence without significant cooling, a glass-forming substance capable of forming an enamel-like coating on said body and melting at the temperature of said body to cause said substance to flow thereon;

thereafter cooling the body and, thereby, simultaneously solidifying the fused substance thereon to form a relatively brittle, temporary enamel-like coating on said body;

stripping the brittle enamel-like coating from the cooled body while straightening same between staggered rolls; and

' applying a protective, relatively nonbrittle permanent anticorrosion coating to said body.

2. A process for making a metal body comprising the steps of:

a. hot rolling a metal bar to reduce the thickness of said bar and increase the length thereof while forming said body;

b. coating said body in a heated state thereof without substantial cooling and immediately following the last of said stages with an enamel-forming powder mixture melting at the temperature of said body, thereby producing a brittle enamel layer prior to the formation of any scale on said body;

c. removing said enamel layer upon cooling of said body below a temperature at which scale tends to form thereon by passing said body between'the staggered rolls of a straightening apparatus; and

d. substantially providing a permanent protective coating on said body.

3. The process defined in claim 2 wherein said body is coated in step (b) with a mixture of reducing-metal powders and finely divided enamel-forming substances which are fused to form said layer solely by the heat contained in said body.

4. An apparatus for making a metal body comprising a rolling mill having a rolling stage for the hot-rolling of a metal bar toreduce the thickness thereof and in-,

crease its length, thereby forming said body; means forming a chamber immediately downstream of said mil and the last of said stages, said body passing through said chamber; means in said chamber for coating said body prior to substantial cooling thereof with brittle-enamel-forming substances meltable at the temperature of said body, the last-mentioned means including a nozzle trained on said body for directing said substances in a dispersion thereagainst, and a pair of blowers in series connected to said nozzle; and a straightening mill having rollers engaging said body downstream from said chamber for breaking an enamel layer formed on said body in said chamber, and means downstream of said straightening mill for coating said body with a permanent protective layer.

5. The apparatus defined in claim 1, further comprising a venturi injector between said blowers and said nozzle and provided with a source of compressed air. 

1. In the production of a metal body wherein the body emerges from a hot-rolling stage in a hot, solid, and relatively scale-free condition, the improvement comprising the steps of: progressively applying to the exterior of said body, as it emerges from said hot-rolling stage in its hot condition prior to substantial scale formation on said body and immediately upon such emergence without significant cooling, a glass-forming substance capable of forming an enamel-like coating on said body and melting at the temperature of said body to cause said substance to flow thereon; thereafter cooling the body and, thereby, simultaneously solidifying the fused substance thereon to form a relatively brittle, temporary enamel-like coating on said body; stripping the brittle enamel-like coating from the cooled body while straightening same between staggered rolls; and applying a protective, relatively nonbrittle permanent anticorrosion coating to said body.
 2. A process for making a metal body comprising the steps of: a. hot rolling a metal bar to reduce the thickness of said bar and increase the length thereof while forming said body; b. coating said body in a heated state thereof without substantial cooling and immediately following the last of said stages with an enamel-forming powder mixture melting at the temperature of said body, thereby producing a brittle enamel layer prior to the formation of any scale on said body; c. removing said enamel layer upon cooling of said body below a temperature at which scale tends to form thereon by passing said body between the staggered rolls of a straightening apparatus; and d. substantially providing a permanent protective coating on said body.
 3. The process defined in claim 2 wherein said body is coated in step (b) with a mixture of reducing-metal powders and finely divided enamel-forming substances which are fused to form said layer solely by the heat contained in said body.
 4. An apparatus for making a metal body comprising a rolling mill having a rolling stage for the hot-rolling of a metal bar to reduce the thickness thereof and increase its length, thereby forming said body; means forming a chamber immediately downstream of said mil and the last of said stages, said body passing through said chamber; means in said chamber for coating said body prior to substantial cooling thereof with brittle-enamel-forming substances meltable at the temperature of said body, the last-mentioned means including a nozzle trained on said body for directing said substances in a dispersion thereagainst, and a pair of blowers in series connected to said nozzle; and a straightening mill having rollers engaging said body downstream from said chamber for breaking an enamel layer formed on said body in said chamber, and means downstream of said straightening mill for coating said body with a permanent protective layer. 